First, patina is defined as the surface appearance of something grown beautiful, especially with age or use, which adds value to an antique or collectible and should not be cleaned.

When working with antique furniture, dealing with dents and dings on the
surface may pose a problem during the finishing process. With
antiques, I take the approach to try and determine which dents
or dings are the result of "use" versus "abuse". This in turn leads me
to a course of action to begin the finishing process and to save as
much of the patina as possible.

Here are some tips to consider when repairing and/or refinishing an antique:

When inspecting the surfaces, look for signs of natural wear and tear.

Old dents and dings are usually smoothed over and have no obvious
sharp edges.

Fresh dents and scratches will usually allow the substrate color
to appear.

Using bright light, look for jagged edges in the finish top coat around dents.
This indicates more recent damage.

The edges of desks and tables usually show signs of wear from long term use
and are usually very smooth.

Abuse is usually in the form of Johnny using said piece as a saw horse or
chopping block or a child's homework is etched into the surface. (Another example,
I used to like playing ping pong on my Mom's dining table!)